The present invention relates to a method of controlling fuel supply to an internal combustion engine at the time of termination of fuel cut off therefor.
When the vehicle incorporating an internal combustion engine is being decelerated, in order to decrease the amount of uncombusted components in the exhaust gas of the engine, and in order to conserve fuel, it is per se conventional to cut off the supply of fuel to the engine. Such a fuel cut off procedure is starterd, typically, when the throttle valve of the engine is set to the idling position but the engine rotational speed is greater than a certain determinate value, which indicates that the engine is not currently idling. Further, such a fuel cut off procedure is terminated, typically, when the throttle valve of the engine is opened from said idling position, or when the engine rotational speed drops below said certain determinate value. It is not acceptable to have any substantial delay in restoring the supply of fuel at the ending of fuel cut off, because in such a case the engine will quite probably stall. In Japanese Laid Open Publications Nos. 55-49537 (1980) and 58-162740 (1983), both of which relate to the electronic fuel injection type fuel supply means for internal combustion engines, it is proposed that, at the same instant as indication of fuel cut off stops, the fuel injector provides an injection of fuel, so that no substantial delays of fuel supply arise.
However, it is not always satisfactory that a constant amount of fuel is injected at the end of fuel cut off as proposed in the prior art. Specifically, the colder the intake air which is being sucked into the engine, the easier it is for the engine to stall; and further, the colder the intake air, the greater is its density, so that more fuel is required in order to provide the correct air/fuel ratio for combustion. Now, since the prior art outlined above has provided a substantially fixed amount of fuel at the end of fuel cut off, this has meant that in some circumstances either too much or too little fuel has been supplied for proper engine operation, and stalling of the engine has thus not been positively prevented. As a consequence of the above problem, the engine revolution speed at the end of fuel cut off has been required to be set higher than would be otherwise desirable.